ADJTIME(2) OpenBSD Programmer's Manual ADJTIME(2)NAME
adjtime - correct the time to allow synchronization of the system clock
SYNOPSIS
#include <sys/time.h>
int
adjtime(const struct timeval *delta, struct timeval *olddelta);
DESCRIPTIONadjtime() makes small adjustments to the system time, as returned by
gettimeofday(2), advancing or retarding it by the time specified by the
timeval delta. If delta is negative, the clock is slowed down by
incrementing it more slowly than normal until the correction is complete.
If delta is positive, a larger increment than normal is used. The skew
used to perform the correction is generally a fraction of one percent.
Thus, the time is always a monotonically increasing function. A time
correction from an earlier call to adjtime() may not be finished when
adjtime() is called again. If delta is null, no adjustment is done. If
olddelta is non-null, the structure pointed to will contain, upon return,
the number of microseconds still to be corrected from the earlier call.
Setting the time with settimeofday(2) will cancel any in-progress time
adjustment.
This call may be used by time servers that synchronize the clocks of
computers in a local area network. Such time servers would slow down the
clocks of some machines and speed up the clocks of others to bring them
to the average network time.
Only the superuser may adjust the time using the adjtime() function.
RETURN VALUES
A return value of 0 indicates that the call succeeded. A return value of
-1 indicates that an error occurred, and in this case an error code is
stored in the global variable errno.
ERRORSadjtime() will fail if:
[EFAULT] Either of the arguments point outside the process's
allocated address space.
[EPERM] The delta() argument is non-null and the process's
effective user ID is not that of the superuser.
SEE ALSOdate(1), adjfreq(2), gettimeofday(2), ntpd(8), timed(8), timedc(8)
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX
4.3BSD.
HISTORY
The adjtime() function call appeared in 4.3BSD.
CAVEATS
Other operating systems restrict calling adjtime to the superuser and
might not allow requesting the current correction without specifying a
new value.
OpenBSD 4.9 June 5, 2009 OpenBSD 4.9
